1. Field of the Invention
The present invention relates to an extractive separation method for separating an extract (a solute) in the supercritical phase thereof wherein the extraction is carried out by means of a solvent in the sub-critical phase thereof.
2. Description of the Prior Art
Recently, the supercritical-fluid extraction is being watched with interest as the separation technique of components in the fields of food chemistry, petrochemical industry and the like. This technique consists in that organic or inorganic substances, which are gaseous at the atmospheric temperature and an atmospheric pressure, are pressurized at temperatures over the critical temperature thereof to increase the density thereof and the extraction is carried out by utilizing the dissolving power thereof improved owing to an increase in the density thereof. They say that this technique is advantageous in respect of energy since it does not require the separation means, which is accompanied with the changes in phase of substances such as cooling and distillation, for the separation of a solute from a solvent differently from the usual liquid-liquid extraction. Industrially, the practical applications of this technique can be found in the extractive separation of various kinds of hydrocarbon and the extraction of ethanol from an aqueous solution of ethanol [Japanese Patent Application Laid-Open No. 56201/1981 (BP 2,059,787, DE-OS 3,033,729), Japanese Patent Application Laid-Open No. 92,674/1983 (BP 2,110,678, DE-OS 3,242,420)], the extraction of perfumes from fruit juice [Japanese Patent Application Laid-Open No. 145,195/1982 (BP 2,091,292, DE-OS 3,101,025), Japanese Patent Application Laid-Open No. 74,797/1983 (DE-OS 3,137,230, EP 75,134)], the extraction of caffeine from coffee [Japanese Patent Publication No. 36,344/1976, (DE-AS 2,005,293), Japanese Patent Publication No. 37,334/1976 (U.S. Pat. No. 3,879,569, BP 1,372,667, DE-AS 2,212,281), Japanese Patent Application Laid-Open No. 69,584/1980 (EP 10,636), the extraction of nicotine from tobacco [Japanese Patent Publication No. 9,838/1976 (DE-AS 2,043,537), Japanese Patent Application Laid-Open No. 107,165/1983 (BP 2,111,371, DE-OS 3,148,335, EP 81,231)], the extraction of essence from hop [Japanese Patent Application Laid-Open No. 45,391/1980 (BP 2,026,539, DE-OS 2,827,002, 2,829,308), Japanese Patent Application Laid-Open No. 89,176/1983 (EP 80,582), the regeneration of adsorbents [Japanese Patent Application Laid-Open No. 31,679/1976, Japanese Patent Application Laid-Open No. 61,484/1976 (U.S. Pat. No. 4,124,528, BP 1,522,352, DE-OS 2,544,116), Japanese Patent Application Laid-Open No. 126,678/1977 (DE-OS 2,716,798)] and the like.
However, these known supercritical-fluid extraction methods consist in the repetition of the operation that a medium is brought into contact with a solvent under a superhigh pressure of for example 5 to 6 times the critical pressure to extract the desired solute contained in the medium and then the solute is separated from the solvent by remarkably reducing the pressure and/or temperature to reduce the dissolving power of the solvent.
In the case where the temperature and pressure in the extraction are so severe, there is the danger that the aimed solute is deteriorated whereby being incapable of obtaining the satisfactory result. In addition, an expensive equipment is required for carrying out these methods since the extraction is largely different from the separation in the conditions. Further, there is room for the improvement in their separation efficiency.